This application claims the priority of German Patent Application No. 100 20 643.3-14 filed Apr. 27, 2000, which is incorporated herein by reference.
The invention relates to an arrangement for the torque-free shifting of a mechanical gearbox.
Until now, the number of engine revolutions, the countershaft revolutions and the output shaft revolutions, as well as the computed engine torque were used as control variables for shifting gears in partially or fully automatic gearboxes. In the case of transmissions where the clutch is not opened for shifting the gears, it is extremely important for reasons of comfort that the transmission is torque-free during the shifting from a gear to the neutral position. An unacceptable torque jolt may otherwise occur as a result of releasing the pre-stressing of a gear wheel and the transmission drive shaft. Detecting the zero passage of the torque with the aid of a computed engine torque curve is not precise enough for this. A sensing of the actually present torque is therefore required.
It is the object of the invention to provide a torque-controlled gearbox, for which the actually present torque at the transmission driving shaft is detected as an additional control variable for the shifting operation.
The above object generally is achieved according to the present invention by an arrangement for the torque-free shifting of gears in a drive assembly with a mechanical gearbox, which arrangement comprises: a mechanical gearbox having a plurality of gears for changing the transmission ratio for the number of revolutions at the input drive shaft of the gearbox and the output drive shaft of the gearbox; a controllable gearshift for actuating the gearbox and selectively engaging the different gears; a gear control unit, which is responsive to input variable control signals, for activating the gearshift; and at least one inductive torque sensor that is installed near the surface of a shaft for the drive assembly. The inductive source sensor includes at least one exciter coil for the induction of a magnetic alternating field in one of the shafts of the drive assembly, and at least two sensor coils. One of the sensor coils detects the magnetic field induced in the shaft in the compression stress direction and the other sensor coil detects the magnetic field induced in the shaft in tensile stress direction, and the two sensor coils are arranged in a difference circuit that provides a difference signal as an output measuring signal for the torque sensor, with the difference signal being fed to the gear control unit as an input variable control signal. Additional advantageous features and embodiments are disclosed and described.
The solution is obtained with a torque-controlled gearbox where the torque present at the transmission driving shaft is measured by a non-contacting torque sensor. The torque sensor delivers a measuring signal that is supplied to a gear control unit as a measure for the correct shifting moment. With a motor vehicle having an internal combustion engine, the drive output of the combustion engine is transmitted to the crankshaft. A clutch transmits the torque present at the crankshaft to the transmission driving shaft, then transmits it from there via an intermediate gear to an output shaft and finally via a differential gear to the drive wheels of the motor vehicle. The torque sensor detects the torque actually present at the transmission driving shaft and feeds the measuring signal belonging to this torque to a gear control unit. The gear control unit is furthermore connected to a revolution sensor for detecting the engine revolutions, to a speed sensor for detecting the vehicle speed and to a gas-pedal sensor for detecting the gas-pedal position. The clutch and the gearbox are activated by driven final control elements actuated by the gear control unit. The gears in the transmission are preferably shifted at those moments where no torque is present at the transmission drive shaft. The zero passage of the torque curve at the transmission driving shaft, measured with the torque sensor, in this case is selected as a measure for the correct shifting moment.
The magneto-elastic effect on rotating shafts subjected to torque is used to measure the torque itself. If a shaft is twisted as a result of a torque, then areas of compressive stress and areas of tensile stress form on the surface of the shaft with torque. The directions for tension and pressure are perpendicular to each other. The magnetic properties of ferromagnetic materials such as steel for producing tools change under the influence of mechanical tensile stresses and compression stresses. These changes in the magnetic properties are measured with the aid of a torque sensor, comprising at least one exciter coil and at least two sensor coils. For this, the sensor is attached near the shaft surface and a magnetic alternating field is generated with the exciter coil, for which the magnetic field lines penetrate the shaft. As a result of the magneto-elastic effect, the size and direction of the magnetic field generated with the exciter coil in the shaft subjected to torque will differ, both in compression stress direction and in a tensile stress direction. One of the sensor coils of the torque sensor detects the magnetic field induced in the compression stress direction, while the other torque sensor coil detects the magnetic field induced in the shaft in the tensile stress direction. The two sensor coils or their measuring signals for the compression stress direction and the tensile stress direction are components of a difference circuit. The torque sensor therefore supplies a difference signal for the compression stress direction and the tensile stress direction. A magneto-elastic effect is not present in the shaft if there is no torque, meaning if the shaft is not subjected to compression stresses and tensile stresses. In that case, the magnetic field shares are equal in compression stress direction and in the tensile stress direction, and the difference signal of the torque sensor indicates a zero passage. The zero passage of the difference signal from the sensor coils of the torque sensor thus indicates a torque-free condition of the shaft and functions as a measure for indicating the suitable shifting moment. The difference signal is used as a control variable for the gear control unit.
The following advantages are primarily achieved with the invention:
The torque controlled transmission according to the invention permits a non-jolting shifting of the gears for semi-automatic or fully automatic transmissions. The mechanical components are thus protected, wear and tear is reduced and the service life of transmission and clutch, in particular, is increased.
The torque detection or the detection of the torque-free condition of the transmission driving shaft for the first time offers the option of shifting gears without torque and thus comfortably, without having to open the clutch. As a result, the torque-controlled transmission according to the invention is particularly suitable for all gearboxes with automatic shifting, for which the clutch remains closed during the shifting of the gears.
However, the torque-controlled transmission according to the invention is also advantageous if the clutch is to be opened during the shifting of the gears. Detecting the torque-free condition is important for those gears as well because, on the one hand, the clutch is released without jolting if the torque present before the clutch release is near zero while, on the other hand, it permits a reliable detection of the clutch opening and whether the clutch has completely separated the crankshaft from the transmission driving shaft. In that case, the gearshift according to the invention also makes it possible to detect the correct shifting moment. In particular, it is possible to detect a clutch malfunction if no torque-free condition occurs despite the fact that the clutch on the transmission driving shaft is engaged. The clutch/transmission system can thus be diagnosed and a dragging clutch detected with the aid of the gear control unit. The clutch does not function properly if the torque sensor in the gear control unit does not show a zero passage of the differential signal as indication of the torque-free condition of the transmission driving shaft, even though the control elements for opening the clutch are activated. Excessive wear resulting from clutches that drag or are incorrectly adjusted can thus be detected and avoided.
Exemplary embodiments of the invention are shown in the following and are explained in further detail.